Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $97.88   6.283%   $104.0298   $104.03   $104.05   $104.00  
  Purchase #2 $207.57   5.857%   $219.7274   $219.73   $219.75   $219.70  
  Purchase #3 $115.62   13.781%   $131.5536   $131.55   $131.55   $131.60  
  Purchase #4 $195.50   5.706%   $206.6552   $206.66   $206.65   $206.70  
  Purchase #5 $216.47   10.565%   $239.3401   $239.34   $239.35   $239.30  
  Purchase #6 $93.37   13.386%   $105.8685   $105.87   $105.85   $105.90  
  Purchase #7 $65.35   12.661%   $73.624   $73.62   $73.60   $73.60  
  7 purchase totals = $991.76       $1,080.7986   $1,080.80   $1,080.80   $1,080.80